There will no flexibility when it comes to the deadline for online self-assessment, warns HM Revenue and Customs.
The 31st January deadline this year falls on a Sunday, with the cut-off point staying firm at 11.59pm.
In 2009 a record 5.8 million taxpayers filed their tax returns online, but that's expected to be topped this year.
Tax experts are urging people not to wait until the last minute as in previous years HMRC's website
has crashed as thousands of sole traders and self-employed workers log on at the same time.
Meanwhile there are fears internet connections in some rural areas won't be able to cope.
Those who don't file their return and pay any tax due by the deadline face a £100 fine.